Research On Wearable CH₄ Gas Sensor Based On Doped-Si/SiO₂ Fiber And Co-doped ZnO Nanorods

Metal oxide semiconductor（MOS）gas sensors have been widely studied and applied due to their advantages of simple preparation process,fast response,high sensitivity,stable performance and low cost.However,MOS gas sensors require high operating temperatures（above 200℃）.At present,the main implementation of its heating unit is the coating or in-situ growth of MOS nanomaterials on ceramic tubes,micro-electro-mechanical system（MEMS）and polyimide（PI）heating substrates.However,these traditional MOS gas sensors are limited in wearable device applications due to their inflexibility and high-power consumption caused by large heat loss.This paper proposes a method to fabricate a flexible MOS gas sensor with low heat loss,low power consumption and small volume by using Doped-Si/SiO₂composite fiber as the substrate.The Doped-Sifiber core was used as the heat source,the SiO₂was used as the insulating substrate,and the Co-doped ZnO nanorods were grown on the fiber surface in situ as the gas sensing material.The Joule heat generated by the current applied to the Doped-Sifiber core is all heated to the MOS gas sensitive material through heat conduction,which makes the sensor have the advantage of reduced heat loss;SiO₂is an insulating substrate commonly used in semiconductor process.It is compatible with the existing semiconductor process and is an ideal substrate material for the in situ growth of MOS gas sensitive materials.Our study demonstrated the feasibility of using Doped-Si/SiO₂fibers as the substrates to fabricate wearable MOS gas sensors,where the sensors have substantial advantages over tradition sensors in flexibility,heat utilization,etc.The research content of this paper mainly includes the following two aspects:1.Fabrication and characterization of Co-doped ZnO gas sensors based on Doped-Si/SiO₂fibers.Firstly,the Doped-Si/SiO₂fibers were fabricated by thermal drawing method and then characterized;after that,gas detection electrodes,ZnO seed layers and Co-doped ZnO nanorods were fabricated on the fiber surface;protective layer of Polydimethylsiloxane（PDMS）with a thickness of 30μm was coated on the surface of the Doped-Si/SiO₂fiber by dip-coating method;finally,the heating electrode was prepared to complete the preparation of the gas sensor.2.Performance testing and wearable integration of CH₄gas sensors.We first introduce the main performance indicators for the evaluation of MOS gas sensors and test systems;after that,the response of the sensor was tested under different temperatures and different CH₄concentrations,and the durability test under different humidity,bending degree,bending times and different days was carried out;COMSOL simulates the temperature distribution inside the Doped-Si/SiO₂fiber and calculates the heat loss of the sensor based on the simulation results;through the space charge layer model,we describe the gas-sensing mechanism of ZnO and Co-doped ZnO;finally,we woven the Co-doped ZnO gas sensors based on Dope-Si/SiO₂fibers on the miner cloth and designed the supporting circuit to connect the sensor.The application of the sensor in wearable direction is demonstrated by controlling different color LED lights to warn different concentrations of CH₄through a circuit board.